Tensions have been rising between the U.S. and Russia ever since President Donald Trump bombed Syria a few weeks ago. That’s why it’s been so alarming that each night this week, Russian military planes have been spotted flying unusually close to the U.S.

Daily Mail reported that Russia sent planes flying towards Alaska each night this week, beginning on Monday. Though the aircrafts stayed in international airspace for the entirety of their journeys, they have gotten as close as 36 nautical miles off the Alaskan mainland.

American military officials have expressed concerns about this given the fact that the Russians haven’t flown this close to Alaska in two years.

It all started on Monday night, when two nuclear-capabe Tu-95 Bear bombers were intercepted by American F-22 fighter jets about 100 miles off the coast of Kodiak Island. On Tuesday night, a pair of the same kind of bombers flew towards Alaska, staying north of the Aleutian Islands. This time, the U.S. Air Force sent a surveillance plane instead of fighter jets to make sure the larger bombers weren’t hiding any stealth planes flying underneath them.

The next night, the Russians sent a pair of Ilyushin IL-38s spy planes near the Aleutian Islands, and the Air Force once again sent surveillance planes to observe. On Thursday night, the Russians sent out two long-range bombers again. This time, Canadians joined the U.S. Air Force in sending fighter jets out to intercept the Russian bombers about 700 miles southeast of Anchorage.

A U.S. official said that there is “no other way to interpret this other than as strategic messaging.”

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